1. Field of the Invention
The present invention relates to a spacer for use with an inhaler for dispensing powdered medicament. Such a spacer may be used to ensure that an effective dose of a discrete amount of medicament is dispensed by the inhaler by reducing drug particles above a predetermined size from the administered dose.
2. Description of the Related Art
Conventionally dry powder inhalers comprise three parts: a reservoir for solid medicament either in a dry powder form or in a form suitable for the generation of dry powder for delivery on demand; a metering device for delivery of consistent doses of medicament from the reservoir; and an outlet.
A patient inhaling through the outlet receives a metered dose of the medicament. Metered dose inhalers allow the patient to administer an accurate does of medicament when required. This is particularly useful during a sudden occurrence of respiratory difficulty, such as an asthma attack.
One problem with dry powder inhalers is to ensure that an effective dose of the medicament is delivered to the patient""s lungs. Dispensed medicament particles tend to separate according to size under the influence of gravity and air currents. Smaller particles, for example less than 5-6 xcexcm in diameter, pass through the patient""s oro-pharynx and enter the trachea, bronchi and lower airways where they are able to exert a therapeutic effect. Larger diameter particles are more likely to be deposited in the patient""s oro-pharynx. Such oro-pharyngeal deposition is undesirable for a number of reasons. The patient may experience an unpleasant taste when particles alight on the mucosa. Furthermore the proportion of the dispensed dose inhaled which actually constitutes an effective dose is reduced. Moreover unwanted deposits of certain classes of compounds may cause undesirable side effects, eg a high incidence of Candida infections (xe2x80x9cthrushxe2x80x9d) has been reported in association with the administration of corticosteroids.
In pressurised metered dose inhalers the larger droplets formed in the aerosol cloud have been separated out by providing a xe2x80x9clarge volume spacerxe2x80x9d to allow these larger droplets to impinge on the spacer wall, evaporate or fall to the floor of the spacer. Such a xe2x80x9clarge volume spacerxe2x80x9d is unsuitable for use with a powder inhaler where the patient""s inspirational air flow withdraws the dose from the inhaler.
Alternatively impact surfaces have been used in order to break up the larger particles of medicament. However this requires a tortuous air path. This results in a bulky spacer and increases the inhalation force required for effective drug delivery. It is undesirable to impose a further burden on a patient who is already experiencing respiratory problems.
The present invention seeks to provide a compact device which reduces the large particle dose without adversely affecting the fine particle dose and hence reduces the amount of oro-pharyngeal deposition of large medicament particles, while allowing self-administration of an effective dose without increasing the respiratory burden on the user.
According to a first aspect of the invention there is provided a powdered medicament inhaler spacer, comprising:
a body defining a chamber;
an inlet communicating with the chamber; and
an outlet communicating with the chamber, in which the chamber, inlet and outlet are adapted to provide a rotational flow path in use for an airstream passing from the inlet through the chamber to the outlet.
In preferred embodiments of the invention the body has a slender curved configuration.
The body may include an internal surface having the configuration of a closed curve. The body is preferably slender, that is of small width relative to its length or height. The body is preferably curved, that is the body may have the shape of a circle, ellipse, ovoid or other closed curve. Alternatively the body may be partially curved, that is with only a section of the body having a curved shape.
The chamber is preferably cylindrical, more preferably a circular cylinder having a horizontal radial axis in use and a continuous curved internal wall with two generally flat sides. Alternatively the cylinder may have the shape of an ellipse, ovoid or other closed curve.
The inlet and outlet communicate with the chamber such that an airstream with powdered medicament entrained in it may pass through the spacer, entering the chamber through the inlet and exiting the chamber through the outlet. The positions of the inlet and outlet are arranged within the chamber such that the airstream has to undergo at least some degree of rotational motion within the chamber in order to pass through the spacer. In preferred embodiments of the invention rotation through 360xc2x0 occurs within the chamber. The curved form of the body together with the slender form of the body cooperate to constrain the possible flow paths of the airstream so that the only flow path possible is substantially rotational, ie the geometry of the spacer body reduces motion in a direction transverse to the body and induces rotational motion in direction parallel to the curvature of the body. The rotational motion in general of the medicament particles causes larger particles to be removed from the airstream.
One particular effect of the rotational motion of the powdered medicament particles in the airstream, is that it causes a centripetal force to act on the particles. The reaction of the centripetal force causes particles to move towards the surface of the chamber. The force acting on the particles is proportional to their mass and consequently the more massive particles, ie those with a greater dimension, experience a greater force and are urged towards the curved surface. As the particles impinge on the internal surface of the walls of the body they tend to adhere to it. In this manner particles above a certain size may be selectively removed from the airstream as it passes through the spacer. Hence, a dose of medicament with particles of the desired smaller sizes may be administered.
The curved body is arranged to induce rotational motion in the airstream without increasing the respiratory effort of the user. The curved body relies on its geometric form to induce a rotational flow path without imparting a sudden change in direction of the airstream flow path. Hence, larger particles are caused to adhere to the inner surface of the chamber. Fragmentation of larger particles may occur releasing further medicament of an inhalable size.
The curved body and chamber may have a transverse or radial axis and a lateral axis. Preferably the dimension of the transverse axis is less than the dimension of the lateral axis, more preferably half the dimension of the lateral axis. The transverse, ie radial dimension of the body is less than the lateral dimension of the body so that the flow path of the airstream is constrained to be substantially rotational. The sides of the body are disposed sufficiently close together so as to prevent substantial transverse flow, but are sufficiently spaced apart as to provide the chamber with a shape that does not significantly impede the passage of an airstream through the spacer so that the spacer does not impose a respiratory burden on the user.
The flow within the spacer may be observed in conventional manner using smoke or other opaque gaseous medicine within a spacer constructed of transparent material
Preferably, the inlet engages the curved body in a first direction and the outlet engages the body in a second direction and the first direction and the second direction lie in a common plane of the curved body which is perpendicular to the transverse axis. In this way, the inlet and outlet are arranged so that they are coplanar and their common plane is substantially perpendicular to the transverse axis of the body. Hence, only those particles undergoing rotational motion rather than transverse motion will be able to pass from the inlet to the outlet. The first direction and the second direction may be parallel.
In certain embodiments of the invention the inlet tangentially engages the curved body or enters the body tangential to the flow path within the chambers. In this way the airstream enters the chamber and is caused to follow a rotational flow path without having to undergo an abrupt change in direction which may cause the impedance of the spacer to air flow to increase. The outlet preferably also tangentially engages the curved body.
In one embodiment the inlet and outlet do not extend within the chamber. This serves to ensure that the inlet and outlet are flush with the inner surface with the flow of the airstream. This reduces turbulence and may avoid unnecessary surfaces to which particles may adhere.
Alternatively one or both of the inlet or the outlet extend within the chamber. In this way the position within the chamber at which the airstream is introduced, or the position at which the airstream leaves the chamber may be selected. This serves to facilitate the delivery of medicament particles within a selected range of sizes to the patient. However, the ends of the inlet and the outlet need not overlap if the distance between them is such that the momentum of the medicament particles in the airstream is sufficient to prevent any direct non-rotational flow from the inlet to the outlet.
The end of the inlet within chamber and the end of the outlet within the chamber may co-terminate. Preferably the end of the inlet within the chamber and the end of the outlet within the chamber overlap. The relative positions of the ends of the inlet and outlet within the chamber may be chosen so as to enhance the removal of medicament particles above a selected size from the airstream.
one or more internal surfaces of the body may be roughened so as to facilitate deposition of the unwanted larger particles. In this way the effectiveness of the spacer in selectively removing larger medicament particles may be increased.
The selectively extracted particles may be larger than a predetermined size. Preferably, the predetermined size is about 10 xcexcm, more preferably about 6 xcexcm, most preferably about 2 xcexcm.
An end of the inlet external to the chamber may be adapted to connect to a medicament delivery outlet of the powdered medicament inhaler. An end of the outlet external to the chamber may include a mouthpiece.
The inlet or outlet may have spirals or other moldings inside to give greater turbulence to the airflow.
The spacer may be made wholly or partially of a transparent material. In this way a user can tell when the spacer needs cleaning owing to an excessive build up of extracted medicament. The spacer may be constructed from two parts adapted to allow the spacer to be easily disassembled for cleaning and reassembled for use. This allows the spacer to be easily cleaned so that optimum performance may be maintained and also ensures that the correct effective dose of medicament is delivered.
The spacer may have one or more protuberances extending transversely across the chamber. The presence of the formation in the chamber will help to induce further turbulence in the airstream passing through the spacer and hence increase the amount of medicament selectively extracted from the airstream.
The protuberances may comprise a plurality of stepped baffles disposed on the side walls of the chamber. The stepped baffles may be opposed so as to form constrictions to the airflow. Alternatively the baffles may be disposed in an alternate relationship so that the airflow is caused to pass alternately from one side of the chamber to the other.
Triangular or wedge shaped baffles may be preferred. These may be arranged to extend inwardly from the planar faces of the cylindrical chamber. The baffles may be arranged either clockwise or anti-clockwise so that the airstream contacts the inclined surface or axially extending surface as desired in order to induce the selected degree of turbulence.
When the spacer is constructed from two parts, the formation may include a fastener to secure the two halves of the spacer together. The fastener may be in the form of a screw co-operating with a thread in part of the formation associated with one of the two parts. The screw may be separate to the formation or an integral part of the formation associated with the other of the two parts of the spacer. Alternatively, the fastener may be in the form of a releasable snap-fit device.
The spacer may be integral with the powder dispenser.
According to a second aspect the invention there is provided a powdered medicament inhaler including a spacer comprising;
a slender curved body defining a chamber;
an inlet communicating with the chamber; and
an outlet communicating with the chamber, in which the inlet and the outlet are arranged so that in use an airstream passing from the inlet through the chamber to the outlet is caused by the slender curved body to follow a rotational flow path so as to selectively extract particles of powdered medicament entrained in the airstream.